U.S. Adults Eating More—& More Often

Jul 14, 2011

Do your overweight and obese clients have trouble losing weight and keeping it off? Part of the problem may be how frequently they eat. Over the past 30 years U.S. adults have been eating larger portions and eating more often, according to a new study by University of North Carolina at Chapel Hill researchers. Their findings help illustrate how Americans’ eating habits are contributing to the country’s obesity epidemic.

“First, the food industry started ‘supersizing’ our portions, then snacking occasions increased and we were convinced we needed to drink constantly to be hydrated,” said Barry Popkin, PhD, the study’s senior author and W.R. Kenan Jr. Distinguished Professor of Nutrition at the UNC Gillings School of Global Public Health.

The study is believed to be the first to examine the combined contribution of changes in three key factors—portion sizes, food energy density and eating frequency—on people’s total calorie consumption. The findings appeared in the June 2011 issue of PLoS Medicine.

Study Findings

In the study, Popkin and Kiyah Duffey, PhD, postdoctoral fellow at the UNC Interdisciplinary Obesity Center, analyzed U.S. adults’ dietary intakes over four separate 24-hour periods, based on surveys taken in 1977–1978, 1989–1991, 1994–1998 and 2003–2006. The researchers found that the average daily total energy intake, measured in calories (kcal), increased from 1,803 kcal in 1977–1978 to 2,374 kcal in 2003–2006, an increase of about 570 kcal.

Increases in the number of eating occasions (meals and snacks) and in the portion sizes of foods and beverages over the past 30 years accounted for most of the change. Changes in the energy density of foods and beverages (i.e., the number of calories in a specific amount of an item) contributed a slight decrease in daily total energy intake over the 30-year study period.

In daily total energy intake, portion size accounted for an annual increase of nearly 15 kcal between 1977–1978 and 1989–1991, whereas changes in the number of eating occasions accounted for an increase of just 4 kcal per year. Then, between 1994–1998 and 2003–2006, changes in the number of eating occasions accounted for an annual increase in daily total energy intake of 39 kcal, whereas changes in portion size accounted for an annual decrease of 1 kcal. The average energy density of foods and beverages remained steady between 1977–1978 and 1989–1991, then declined slightly between 1989–1991 and 1994–1998.

A Way to Prevent Obesity

As participants in the surveys may have under- or over-reported the amount of food they consumed, the findings may not be completely accurate, Popkin noted. “Still, these findings suggest that efforts to prevent obesity among adults in the U.S should focus on reducing the number of meals and snacks people consume during the day and reducing portion size as a way to reduce the energy imbalance caused by recent increases in energy intake,” he said. “I would speculate that the same advice would apply to other developed countries.”